1. Field of the Invention
The present invention relates to optical connectors, and more particularly to an optical connector disposed at an end of an optical fiber transmission line.
An optical connector is disposed at an end of an optical fiber cord and is connected to an associated device. When the device is maintained, the optical connector is disconnected therefrom. When the optical connector is disconnected from the device, a laser beam emitted by a semiconductor laser and transmitted through the optical fiber is emitted from the end. When one observes the disconnected optical connector, the emitted laser light may damage the eyes of the observer.
It is expected that optical fiber transmission lines reach households of ordinary people in the near future. When people who are not experts perform connection and disconnection of an optical connector to and from a device, they may observe the end of a disconnected optical connector. Accordingly, an extra amount of safety measures must be taken.
Subscriber optical fiber transmission lines that reach ordinary households may not usually be made of a glass but of a plastic. Most probably, optical fibers having a core whose diameter is as large 1 mm may be used. The above-mentioned safety measures must take into account this fact.
2. Description of the Prior Art
FIGS. 1 and 2 show an optical connector 10 shown in Japanese Laid-Open Patent Application No. 5-288957. The optical connector 10 is constructed such that a ferrule composite 12 is built in a substantially cylindrical housing 11. The optical connector 10 is adapted for a single mode fiber which is used widely in optical communication. A single mode fiber is made of a glass and its core has a diameter of 10 .mu.m.
The ferrule composite 12 is generally constructed such that a first ferrule 14, a second ferrule 15 and a coil spring 16 are built in a cylinder 13. An optical fiber 18 at the end of an optical fiber cord 17 is inserted into the first ferrule 14 fixed therein. An optical fiber 19 is inserted into the center of the second ferrule 15 and fixed therein. The second ferrule 15 is disposed before the first ferrule 14 so as to be aligned therewith and axially displaceable. The coil spring 16 is provided between the first ferrule 14 and the second ferrule 15 so as to urge the second ferrule 15 in the X1 direction, that is, toward the outside of the cylinder 13.
As shown in FIG. 2, in a state in which the optical connector 10 is coupled to a device, the second ferrule 15 is pressed toward a ferrule 20 of the device. The coil spring 16 is compressed and displaced in the X2 direction with respect to the cylinder 13. As a result, an end surface 21 of the second ferrule 15 comes into a close contact with an end surface 22 of the first ferrule 14. A laser beam transmitted through the optical fiber cord 17 passes through the close contact portion and enters an optical fiber 19 in the second ferrule 15. After passing through the optical fiber 19, the beam enters an optical fiber 23 in the ferrule 20 in the device.
When the optical connector 10 is disconnected from the device, the ferrule composite 12 returns to a state shown in FIG. 1. More specifically, the second ferrule 15 is displaced by a distance of L1 in the X1 direction with respect to the cylinder 13 so that the end surface 21 of the second ferrule 15 is detached from the end surface 22 of the first ferrule 14.
The laser beam that left a semiconductor laser apparatus (light source) and is transmitted through the optical fiber cord 17 is diverged at the end surface 22 of the first ferrule 14 and emitted outside the optical cord 17.
It is to be noted that the optical fibers 18, 19 and 20 are usually made of a glass and are extremely thin. Referring to FIG. 3, the diameter d1 of a core 24 of the optical fibers 18, 19 and 20 is usually 10 .mu.m. Therefore, even if the distance L1 is as small as 0.1 mm, only a limited portion of a laser beam 25 diverged at the end surface 22 of the first ferrule 14 and emerging therefrom enters the optical fiber 19 of the second ferrule 15. In this way, the optical intensity of the beam that emerges from the other end of the second ferrule 15 is reduced to a degree that it does not hurt naked eyes.
However, the following problem arises if the conventional optical connector 10 is applied to a subscriber optical fiber line.
An optical fiber 30 predictably used in the subscriber loop system is made of a plastic. As shown in FIG. 4, the diameter d2 of a core 31 is as large as 1 mm. For this reason, a major portion of the laser beam 32 diverged at an end surface 22A of a first ferrule 14A and emerging therefrom enters a core 34 of an optical fiber 53 of a second ferrule 15A, even if a separation L2 of 1 mm is allowed to exist between the first ferrule 14A and the second ferrule 15A. Therefore, it is difficult to reduce the light intensity of the beam emerging from the other end of the second ferrule 15A to a satisfactorily low level. Extending of the separation L2 between the first ferrule 14A and the second ferrule 15A to, for example, 10 mm enlarges the degree of reduction of the light intensity. However, such an arrangement causes the size of the optical connector to be great and is not practical.